Theoretical and experimental analyses of various aspects of cell locomotion have been undertaken over the past few years. These have included formulation of mathematical descriptions of the macroscopic response that moving cells show in response to chemical stimuli in order to understand the relationships between the net movements of a population of cells and the underlying stochastic motile behavior of individual cells within that population. Such information is useful in interpreting the results of in vitro assays for leukocyte chemotaxis. Other aspects of this project include development of laser light scattering techniques for measuring the motility of flagellated bacteria and other swimming microorganisms. We also have been concerned with devising dynamic light scattering schemes for probing the mechanical properties of cytoplasmic gels. Current emphasis is on formulating mathematical descriptions of the sequence of biophysical phenomena involved in the transduction of information about chemical gradients into the locomotory response of chemotactic bacteria.